Reticulated plastic foams are gaining in popularity as filter elements for internal combustion engines and various other applications where air or oil must be filtered to remove particulate contaminants prior to use. These filters generally consist of slabs of a plastic foam whose cells have been reticulated to form an open network of pores permitting flow-through of fluids while retaining particles of dust and grit. These slabs are manufactured in varying thicknesses and pore sizes depending on the type of service for which they will be used, taking into consideration the quantity and particle size range of the contaminants and the viscosity and flow rate of the liquid or gas which must pass through the slab. Multiple layers of varying porosities and thicknesses are frequently used.
The advantage of reticulated foam filter elements is that they offer a high capacity for particulate retention and yet have a prolonged permeability to the passing fluid. In addition, they are capable of being fully regenerated.
When mounting these filter elements in the fluid stream, one must seal the edges to prevent bypass and form a mounting frame which suspends the filter element in the air stream. In the optimum case, this would be achieved by a sealing gasket around the periphery of the element which does not distort the shape of the element or cover any of the surface or reduce the area of the filter element.
Closed-cell (or at least unreticulated) polymeric foams are favored as the gasket material since they can be cured in a mold conforming to any desired shape. A further advantage of these foams is that they bond directly to the reticulated filter element in a secure manner as they are curing. Forming a gasket with these foams along the edge of a slab of preformed reticulated foam is problematic, however, since the foam-forming liquid used to form the gasket permeates the open pore network of the filter element. This is a waste of the sealing material and it reduces the amount of exposed filter element available for filtering and forms a skin on the filter surface that is very restrictive to air passage.